The invention relates to a two-port cartridge type seat valve.
For approximately thirty years, two-port cartridge valves have been widely used in hydraulic control technology as pressure-control, directional or check valves. Such cartridge valves are described in detail, for example, in the article "Cartridge check valves: New option for hydraulic control" by David C. Downs, in "Machine Design", Vol. 52, No. 28, of 11th Dec., 1980, Cleveland USA, pages 143-147. A positive-seating, two-port cartridge valve is likewise described in German Offenlegungsschrift DE-A-36 19 927.
Such two-port cartridge valves are used in a manifold that has a stepped bore and first and second main flow channels. The stepped bore has a first bore step that is connected to the first main flow channel and a second bore step, with a larger diameter than the first bore step, that is connected to the second main flow channel.
The typical two-port cartridge type seat valve includes a valve sleeve that is inserted into the stepped bore, a poppet fitted in the sleeve for sliding axial displacement, a closure spring that biases the poppet into sealing engagement with a valve seat in the valve sleeve, and a valve cover. The valve sleeve has first and second ends, with a first cross-sectional portion at the first end that sealingly fits axially into the first bore step, and a second cross-sectional portion that sealingly fits axially into the second bore step. A central cross-sectional portion between the first and second cross-sectional portion defines an annular chamber within the second bore step, into which the second main flow channel opens when the valve sleeve is inserted into the stepped bore. The sleeve also has an axial main flow bore that forms a first main port in the first end of the valve sleeve and lateral second main ports in the central cross-sectional portion for connecting the main flow bore with the annular chamber. The valve seat is disposed in the main flow bore between the first and said second main ports.
The poppet has first and second ends, with the first end having a closure cone that sealingly engages the valve seat in the valve sleeve. The poppet is biased closed by the closure spring.
To make the two-port cartridge valves interchangeable, the diameters and depths of the stepped bore, the position of the lateral second main flow channel in the manifold, and the dimensions of the valve cover and the position of its fastening screws and pilot connections, are set out in standards for the different nominal valve sizes. In Germany, for example, the relevant standard is DIN 24342. As a result, the external shape of the valve sleeve is substantially predetermined and the person skilled in the art has little scope for adapting the valve to different functions.
Known valves have a cylindrical guide bore that extends from the valve seat axially through the valve sleeve to the second end of the valve sleeve. The poppet is fitted in the guide bore for axial displacement in the valve sleeve. Within the guide bore, a pilot chamber is defined axially by the second end of the poppet. The second end of the poppet accordingly forms a pilot pressure area, S.sub.X, equal to the cross-sectional area of the guide bore.
The maximum possible cross-section of the guide bore is dictated by the minimum necessary wall thickness of the valve sleeve in its central cross-sectional portion and the necessary free cross-section of the annular chamber in the region of the second main port. Accordingly, the maximum possible pilot area S.sub.X, the maximum possible cross-section of the poppet, and therefore the maximum possible free cross-section S.sub.A of the valve seat are also fixed. The free cross-section S.sub.A of the valve seat must, of course, be smaller than the cross-section of the poppet's closure cone which, in turn, cannot be larger than the cross-section of the guide bore.
Such two-port cartridge valves with a maximum free cross-section S.sub.A for the valve seat are used as pressure-control valves. In this application the valves should have a maximum flow capacity. Therefore, the pilot area S.sub.X (which is fixed by the cross-section of the guide bore) is preferably approximately equal to the free cross-section S.sub.A of the valve seat.
However, two-port cartridge valves can also be used as pilot-controlled two/two-port directional valves for switching applications. For such applications, the maximum free cross-section SA of the valve seat is reduced by about 35% to 50%, to reduce the hydrostatic force acting on the poppet in the opening direction, rendering the switching behavior of the valve as much as possible independent of pressure fluctuations in the first main flow port. Consequently, the flow capacity of the valve is reduced by about 35% to 50%, or the valve produces a greater pressure loss. There is thus a need for a two-port cartridge valve that provides a switching function with a high flow capacity.